Discussion of Background
Image forming apparatus, such as printers or photocopiers, include a photosensitive member, typically in the form of a photosensitive drum. The performance of the photosensitive drum is of critical importance, since the image being produced (or reproduced) is formed and developed on the drum. The developed image is then transferred from the drum to, for example, a sheet of paper. Typically, the drum is formed of metal, such as aluminum, and the metal is anodized or coated to provide a thin dielectric layer. The drum is then coated with photo generation and photo conduction layers over the dielectric layer.
In forming an image, the drum is rotated, and a given location on the outer surface of the drum is thereby rotated past a charge roller, an exposure location, a developing location (at which toner is applied), a transfer location (at which the toner image is transferred from the drum to paper), and a cleaning location at which a cleaning blade removes excess toner from the drum so that the process can be repeated. During an image forming operation, as a result of the rotation of the photosensitive drum, and its interaction with the various other components of the image forming apparatus, noise and vibration can occur. For example, vibration (and associated noise) can occur from the rotation of the drum, and any imperfections of the drum, the gear flanges attached to the drum, and/or the drive that interacts with the gear flanges of the drum. Further, an alternating current (AC) electric field is applied to the charge roller, and the alternating current can also cause noise and/or vibration of the drum or between the drum and other components. Further, as the drum rotates past the cleaning blade (which is in contact with the drum), noise can be generated, particularly if the drum is vibrating. This interaction between the drum and cleaning blade is also known as chatter vibration or "stick-slip" vibration. (See, e.g., Chatter Vibration of a Cleaner Blade in Electrophotography, by Kawamoto, in the January/February 1996 issue of Journal of Imaging Science and Technology.)
The noise and vibration associated with operation of a photoconductive drum not only presents an annoyance to workers using (or in the vicinity of) the image forming apparatus, but also, the noise/vibration can lead to image deterioration, distortion, or damage to the apparatus. In particular, the vibration can result in poor performance or interaction between the photosensitive drum and one or more of the components with which the drum interacts, including the cleaning blade, the charge roller, the developer device, etc. For example, if the cleaning blade does not properly remove residual toner, undesirable toner spots can occur in subsequent images. Further, if the drum is not charged or developed properly, the resulting image can have white spaces where the image has not been properly formed, developed or transferred, or black spots where undesired toner has been transferred to the sheet of paper. Noise problems can also occur as a result of the generation of gases (ozone) which occurs during an image forming operation, however this noise is typically relatively small.
To reduce or eliminate noise and/or vibration, the physical characteristics of the drum can be modified, for example, by increasing the thickness of the drum. Thus, the drum can be designed so that its natural frequency differs from that of other components of the apparatus and/or that of the process cartridge (the unit within which the drum is disposed). As a result, the vibrations are eliminated or reduced, or the frequency of the noise which might occur can be shifted so that it is outside of the audible range. However, increasing the thickness of the tube or the "substrate" (that eventually would be coated to be used as an electrophotographic drum) can make the tube more expensive to manufacture, particularly if the tooling utilized to manufacture a tube must be replaced. Moreover, when photosensitive drums are manufactured as replacement parts, they will often be inserted into the process cartridges of another manufacturer. The process cartridge could be refurbished or a newly manufactured replacement process cartridge of a different manufacturer than that of the photosensitive drum, and the manufacturer/refurbisher of the process cartridge could change (or the design of a given manufacturer/refurbisher could change). Thus, it can be difficult to simply select a thickness of the tube which will be suitable for avoiding noise problems, since even if a thickness is selected for a certain process cartridge, that thickness could be unsuitable for another process cartridge. As a result, noise problems can be particularly problematic with photosensitive drums manufactured as replacement parts.
A further difficulty which can arise with photosensitive drums is that the roundness or circularity of the tube can vary over time, which can also lead to image deterioration. The roundness or circularity of the drum can more rapidly deteriorate if the drum is vibrating and contacting other components disposed about the drum. This problem can also be reduced by providing a thicker drum, however as discussed above, increasing the thickness of the drum can increase the materials and manufacturing costs, and/or the requirement for new tooling.
An alternate solution which has been utilized in the past for solving noise and/or vibration problems has been to insert plugs within the photosensitive drum. With this approach, a cylindrical object is inserted into the drum, and the insert provides additional weighting to the drum to alter the mass/frequency characteristics of the drum. However, the separate insertion of plug-type inserts is undesirable for a number of reasons. First, the plug is often required to be positioned at a precise location within the drum, which can complicate the manufacturing process. Further, the plug must be secured in place, which can require the use of an adhesive, thus further complicating the manufacture/assembly process. An interference fit can also be provided between the drum and plug, however, an interference fit could result in deformation of the drum. A further disadvantage that can occur with plug inserts, is that the plug and/or its associated adhesive, can alter the performance characteristics of the drum. Prior inserts have also been disadvantageous due to the costs associated with the design and manufacture of a separate part. In particular, the insert must be designed and capital costs are incurred in designing and purchasing the tooling required to manufacture a part which must be compatible in form and size with the photosensitive drum. The inserts must then be kept in inventory in sufficient quantities.
In view of the foregoing, a device and method are needed for reducing noise and/or vibration in an image forming apparatus, particularly noise and/or vibration associated with operation of a photosensitive drum. Such a device and method are preferably suitable for use in both original equipment and for replacement parts. In addition, such a device and method should preferably minimize the cost to manufacture the insert and a drum including such an insert and should also preferably simplify the manufacturing process.